1. Field of the Invention.
This invention relates in general to a redundant power supply system, and more particularly to a 2N redundant power system and method using cross-coupled AC power transfer.
2. Description of Related Art.
Modern-day communication and computer equipment utilize solid state integrated circuits technology to transmit and control data and switching information. Circuits utilizing solid state integrated circuit technology are highly susceptible to variations in electric power from some desired standard. The power to energize these circuits can be readily derived from commercial AC power. The signal consistency of commercial AC power, however, is unreliable due to user demand and other extraneous considerations causing power level fluctuations. These signal variations can take the form of blackouts, brownouts, or transient interruptions or surges. Power outages that extend for a long period of time, on the order of seconds and longer, can render computer peripheral equipment as unavailable.
Typical subsystems are designed to ride through power outages that last up to 20 milliseconds. If the subsystem is designed for battery backup, the system can continue to operate for several minutes before the unit shuts off due to the batteries discharging. Unfortunately, some power outages can last for an extended period of time beyond the holdup capabilities of the batteries. Therefore, customers have required subsystems that are designed to accommodate two separate incoming power line cords. With two separate incoming power line cords, in the event of a power loss on one power cord, the second power cord will deliver the necessary power to keep the subsystem operational. The main reason for this requirement is that customers want the most reliable equipment that they can get due to the high costs, to the customer, associated with the subsystem being down.
Previous designs have also provided increased fault tolerance. To overcome the problems with the single power line cord, subsystems have been designed with a 2N power system. In other words, each power line cord would have its own separate power system. Therefore, in the event of a power outage on one line cord, the second line cord's power system is capable of powering the entire subsystem.
A 2N redundant power system is a system having two power line cords per load, wherein each powerline cord has its own power system, i.e., twice the reliability. Thus, in the event of a power failure on one line cord, the second line cord's power system powers the entire system. In a 2N redundant power system, the loss of one AC sources increases the stress levels on the power supplies by 100%. Also, the load must be kept within a specified temperature range. To accomplish this, cooling devices are used. If AC cooling devices are used, the increase of stress levels is even more drastic since the AC cooling devices must also be powered by the second line cord in event of a failure to the first power line cord. This reduces reliability and forces severe de-rating of components. It can be seen that there is a need for two cross-coupled AC Transfer switches that always connect power converting hardware to an active AC source.
It can also be seen that there is a need for a 2N redundant power system that prevent changes in the operating conditions when the loss of one AC source occurs.